Sarcomas

Soft tissue and bone sarcomas — a heterogeneous group of mesenchymal malignancies united by histologic origin but diverse in molecular drivers, treatment, and prognosis

Key Points

• Sarcomas are malignant tumors of mesenchymal origin (connective tissue, muscle, bone, fat, nerve, and blood vessels), comprising >70 distinct histologic subtypes; they account for ~1% of adult and ~15–20% of pediatric malignancies.
• Soft tissue sarcomas (STS) account for ~13,590 new cases/year in the US; osteosarcoma and Ewing sarcoma are the most common primary bone sarcomas in children and young adults.
• Molecular diagnosis is essential: specific translocations (e.g., SS18-SSX in synovial sarcoma, EWSR1-FLI1 in Ewing, MDM2/CDK4 amplification in well-differentiated liposarcoma) define subtypes and guide therapy.
• Complete surgical resection with negative margins (R0) is the cornerstone of curative intent; limb-sparing surgery with neoadjuvant/adjuvant radiation is standard for most extremity STS.
• Anthracycline + ifosfamide-based chemotherapy is the backbone of systemic therapy; histology-specific regimens (gemcitabine/docetaxel for uterine LMS, trabectedin for liposarcoma/LMS, eribulin for liposarcoma) reflect the importance of subtype-directed treatment.
• Tazemetostat (EZH2 inhibitor) is FDA approved for INI1/SMARCB1-negative epithelioid sarcoma; other targetable drivers include ALK fusions in IMT, NTRK fusions, KIT/PDGFRA in GIST, and PDGFB fusions in DFSP.
• GIST is treated with imatinib and TKI sequencing — not anthracycline chemotherapy — and is a critical histology-specific distinction from other STS.

Epidemiology & Classification

Sarcomas are rare malignancies of mesenchymal origin that collectively represent ~1% of adult cancers but ~15–20% of pediatric solid tumors. Approximately 13,590 new cases of soft tissue sarcoma and 3,970 new cases of bone sarcoma were projected in the US for 2024, with ~5,150 and ~2,060 deaths respectively. The WHO Classification of Soft Tissue and Bone Tumors (5th edition, 2020) recognizes >70 distinct histologic subtypes, broadly grouped by differentiation: Most common adult soft tissue sarcoma subtypes: • Undifferentiated pleomorphic sarcoma (UPS): Formerly MFH; most common in older…

Molecular Biology & Pathology

Molecular characterization is indispensable for accurate sarcoma diagnosis and subtype-specific treatment. Sarcomas can be grouped by molecular mechanism: Translocation-driven sarcomas (generally younger patients, often lower grade): • Synovial sarcoma: SS18-SSX1 (biphasic) or SS18-SSX2 (monophasic) — detected by FISH or RNA fusion panel. • Myxoid/round cell liposarcoma: EWSR1-DDIT3 (FUS-CHOP) fusion; round cell component (>5%) predicts aggressive behavior. • Ewing sarcoma: EWSR1-FLI1 (85%), EWSR1-ERG (10%), or other EWSR1-ETS fusions. • Alveolar rhabdomyosarcoma: PAX3-FOXO1 (~70%) or…

Clinical Presentation & Staging

Clinical presentation varies markedly by anatomic location and histology: Soft tissue sarcoma presentation: • Extremity STS (~50%): Painless, deep-seated, enlarging mass; >5 cm and deep to fascia are high-risk features; pain occurs late and may indicate neurovascular involvement. • Retroperitoneal STS (~15%): Often very large at diagnosis (median >15 cm) due to absence of early symptoms; abdominal fullness, early satiety, flank pain; most commonly WDLPS/DDLPS or LMS. • Truncal and head/neck STS (~15%): Chest wall, abdominal wall, paratesticular, head/neck. • Visceral STS: GIST (GI bleeding,…

Localized Disease Treatment

Surgery: • Wide local excision with negative (R0) margins is the foundation of curative therapy for all sarcoma subtypes. • Limb-sparing surgery is achieved in >90% of extremity sarcomas with modern technique; amputation is reserved for truly unresectable cases and does not improve survival over limb-sparing surgery + RT. • Retroperitoneal sarcoma: Multivisceral resection (kidney, colon, psoas, adjacent vessels as needed) is necessary to achieve clear margins; repeat surgical resection for local recurrence is often feasible and beneficial for WDLPS. Radiation therapy: • Standard for…

Advanced & Metastatic Disease Treatment

First-line systemic therapy for advanced/metastatic STS: • Doxorubicin 75 mg/m² every 3 weeks (single agent): Standard first-line for most advanced STS subtypes; ORR ~10–25%, median PFS ~4–6 months. • Doxorubicin + ifosfamide: Higher ORR (~26% vs. ~14% vs. doxorubicin alone in EORTC 62012) but no OS benefit; greater toxicity; reserved for cases where tumor response/downstaging is needed. • GIST (entirely distinct TKI-based algorithm): Imatinib 400 mg daily (first-line; exon 9 KIT mutation: 800 mg); sunitinib (second-line); regorafenib (third-line); ripretinib (fourth-line); avapritinib…

Histology-Directed Second-Line Regimens

Once first-line anthracycline-based therapy fails, soft tissue sarcoma treatment becomes highly histology-driven. The subtype dictates which agent offers the best chance of response, so identifying the precise histologic (and, increasingly, molecular) diagnosis is essential before choosing the next line. The table below summarizes the subtype-directed second-line options, matching each agent to the histology in which it has the strongest supporting evidence.